Recently, a hybrid topology power converter with a three-level circuit module and a cascaded H-bridge circuit module was developed. The hybrid topology power converter has the topology of a large-power multi-level converter. For designing this hybrid topology power converter such as a static Var generator (SVG) or a high voltage inverter, the ripple voltage and the ripple current of the bus capacitor and the energy loss of the power elements should be taken into consideration.
Some methods of reducing the ripple voltage or the ripple current of the bus capacitor were disclosed. In a conventional method, the capacitance of a bus capacitor is increased or the number of capacitors is increased. Consequently, the bus ripple voltage is reduced, and the ripple current of each capacitor is reduced. However, if the capacitance of the bus capacitor or the number of capacitors is increased, the overall volume and the fabricating cost of the hybrid topology power converter are increased.
Moreover, the energy loss of the power element can be reduced through a soft switch design. However, it is difficult to achieve the soft switch design of the hybrid topology power converter because the soft switch design is complicated, the energy loss reduction is small and the conduction energy loss cannot be effectively reduced.